Schizophrenia (SZ) is believed to be a disorder of neural connectivity involving the prefrontal cortex. Several lines of evidence have suggested that abnormal synaptic reorganization, such as synaptic pruning, may underlie the pathology of SZ. We previously reported the localization of DISCI, a major risk factor of SZ, in the postsynaptic density in mature neurons. We then demonstrated that DISCI is required for proper maintenance of the synapse and spine by functionally linking to activation of NMDA-type glutamate receptor and conveying the signal to Kalirin-7 (Kal-7) and Rac1. Consistently, several groups, including ours, have obtained preliminary results that DISC1 mutant animal models show a decrease in the spine density in the cortex in adulthood. Considering a peak of DISC1 expression observed in early adolescence and importance of synaptic pruning possibly in the pathology of SZ, we now hypothesize that the DISC1-Kal-7- Rac1 cascade may, at least in part, play a role in the pathology of SZ, especially during the prodromal stage of the disorder in adolescence. We will have four aims as follows: (1) to examine synaptic disturbances in the cortex in several DISC1 mutant animal models in the developmental course from early adolescence to adulthood; (2) to identify whether the deficits of the pyramidal neurons, especially those associated with the spine, primarily lead to circuitry deficits of the frontal cortex and behavioral deficits relevant to SZ; (3) to test whether modulation of PAK1 (a key downstream mediator of Rac1) protects against DISC1-elicited synapse deterioration; and (4) to examine molecular profiles in the frontal cortex of DISC1 mutant animal models, especially those in the pyramidal neuron layers. Through these studies, we wish to characterize SZ-relevant synapse pathology in DISC1 animal models, identify mechanisms of how synaptic disturbance can lead to circuitry defects and behavioral abnormalities, pin down a way of intervention against the synapse pathology (towards therapeutic strategies), and establish changes in the molecular signature associated with the synaptic changes towards biomarker identification.